Casting metals



Feb. W43. J. DORNAUF 2,31%766 CASTING METAL Filed Oct. 17, 1939 2 Sheets-Sheet 1 [E1 Q2 is Fek. 9, 1943;

J. DORNAUF CASTING METAL Filed Oct. 1'7, 1.939 2 Sheets-Sheet 2 0 W m, m

[aad/ enads MIMI/lama INVENTQR TTORNEYS under pressure to reduce which had their fled with sodium.

I alloys.

liosef Dewy we at lll vested m Application ill lln cavities.

e production of dense castings free from pores is especially desirable for delicate castings which must be machined and used, for example,

as aircraft motor housings. Particular dimculty has eed in the casting of All-Si alloys modi- -wherein the porosity of the casting is not altogether caused by the gases developed in the melt, as in the castings produced from ordinary metals and alloys thereof.

Great waste has heretofore existed because many castings h to be discarded as being too porous, and thus too week. he shapes machined from such castings are often used in places where they are subjected to vibration, it is very important toobtain a dense casting of great durability and resistance to fatigue.

it is an object of this invention to produce a dense casting.

A further object of the invention is to produce a very dense casting from light metals, especially such metals as aluminum or aluminum it further object of the invention is to develop a practical method of casting alloys of aluminum d silicon, especially'when modified with sodiurn, so that a very dense casting is obtained.

a further object of duce a novel process of msting light metals under pressure wherein both the castingcrucible the mold and the metals in the crucible and mold are placed under substantially the same ssure and castings are obtained. which ar substantially free of pores, can be ort-on-tha' will i Alien operty to or it, lets, do No. 29t,tl ecernber l, 19%

- (cl. ec-zoei Gil as mourn methods produced castings advantages of decreased porosity odset by the creation of enlarged internal is preferable this invention ls'to proreadily machined, and have unexpectedly great strength.

* nerally, these objects of the invention are obted by placing both the crucible containing the melt and the mold under pressure. which can as '20 atmospheres in excess of atmospheric pressure, and causing the molten etal to how from the crucible into the mold while both are subjected to this pressure.

process diders from the prior art methods new to as great in a - at any convenient plate, as

that both the metal in the melting pot and the mold are under the same pressure, whereas in mown former methods, the metal in the mold alone had an increased pressure applied to it after the metal had been poured therein.

The process in this invention is described in greater detailin connection with the accompanyingdra in which:

Fig. 1 is a cross-sectional view of an apparatus which may employed in the use of the castmg processof this invention.

Fig.3 is a photomicrograph oi a casting produced by this invention. 1

Fig. 3 is a photomicrograph or a casting of metal similar to that of Big. 2, but cast by conventlonal methods.

Fig. d is a diagram of Wiihler curves comparing metals cast by an old method and by this invention.

In Fig. l, a pressure chamber is shown which consists of a housing l, having a removable top i by bolts to. Compressed through pipe and valve t. Safety valve ii and connected to the chamber through cover 2. A

pressure gauge it are mold d, shown as an ordinary sand mold, is placed within the pressure chamber. Before top 2 is put in place, a crucible l containing molten metal is therein, is lowered into place on top of the mold and surrounded by a protective insulating shield d, which may be of asbestos: It to have the crucible l preheated before the molten metal is poured lowered into the chamber. Crucible l includes a removable plug t in the bottom thereof, which plug is connected by pin tdto a handle lib ex:- tending through cover 2. After the crucible i has been placed within the chamber and the handle db connected to plug d, air, or other pressure producing medium, is admitted into the chamber through valve 3. A pressure ranging from 5 to 20 atmospheres in excess of atmospheric pressure is built up within the flow into the mold. It is noted that the pressure is appliedto the metal in both the crucible and the mold. After the metal has solidified in the mold, the pressure is released from the chamber and-the mold removed therefrom.

Repeated tests have proved that this method of casting is applicable to alloys of varying compositiom'and is a practical method for foundry use. No dimculty is experienced in pouring the melt into the mold, and there is no chance of the melt partially solidifying in the mold before the pressure is applied. Thus a uniformly increased density throughout the whole casting is obtained.

therein and chamber before plug t is pulled and the metal allowed to V were cast at a pressure of 8 atmospheres in enexcept those relating to the pressure. Test pieces were machined from these cast bars, and the test pieces from the bars cast under pressure showed an improved dense surface. Table I gives the composition of the alloy, and Table II shows the breaking strength of the bars.

It is clear from the results set forth in the tables that remarkable increases in tensile strength were obtained in each instance where the bar was cast according to the new method.

The increased density of the castings permitted machined shapes to be produced which had firm dense surfaces.

A particularly advantageous discovery of the invention lies in that increased density is obtained in casings of aluminum silicon alloys which are modified with sodium, it being noted that the sodium gives a porosity which is entirely diiferent from the usual piping or porousness caused by imprisoned gases in the casting. This particular porosity occurs in the interior of the casting, while the outside surface is dense, and the porous interior is exposed when the casting is machined. I'hus, aluminum silicon alloys modified with sodium, while verydesirable for delicate castings, have been very expensive in view of the waste incurred in the machining of the castings, which necessitated the remelting of-a great many castings. Even the addition of salts having a degasifying eii'ect upon the melt failed to improve materially the denseness of the interior of the castings. Again, the most improved aluminum silicon alloys with further additicns of Mg, Mn, and the like, were too porous to be completely successful.

It was discovered that when such aluminum silicon alloys modified with sodium were cast according to this invention, a remarkably dense was melted at a temperature of 780 0. and was treated with 0.06% Na. Immediately after the addition of sodium, the melt was poured into a preheated crucible, and the crucible placed together with the mold in a pressure chamber. A pressure of 5 atmospheres in excess of atmospheric pressure was built up in thechamber before the plug was drawn from the crucible and the molten metal flowed into a sand mold. The casting was removed from the mold after it had solidified.

Fig. 2 is a photomicrograph of a section of the casing thus obtained. This casting is substan tially free of pores, and is very dense.

In comparison with this casting of the aluminum silicon alloy treated with sodium, a similar casting was made of the same dimensions and composition, with the casting being done by conventional methods. Care was taken that the melting and the casting operation and also the time periods before and after the addition of TableI A110 Designaf on Zn Cu Mg s1 Ni Mn sb Fe Ti Per Per Per a. Per Per Per Per Per 1 Al-Mg si cent cent 07cm amt cent cent emf $01? cent 0 2 Y- llo w i t special additions- .i 2.25 1.6 1.26 1.3 1.4 0.3 0.1 i Y-alloy 4 1.6 2 0.3 4 German alloy.. 10 2 0.5 0.5 5 Alloy re sistant to sea water 2.3 0.6 1.5 0.2 0.3

- "so The remainder of each of alloys 1 through 6 was aluminum.

Table II Casting pressure in atmos $221 3 AlloyNo. pheresgi an excess atmosphericpressure c ia'a a5 5 8 12.0 0 11.4

sodium and the method of pouring the metal into the mold were exactly the same as the pressure casting test. In other words, the same test was run, except that both the crucible and mold were not put under an increased pressure. The result of this test is shown in Fig. 3, which is a photomicrograph of a section of the bar obtained. This photomicrcgraph shows many pores in the casting. By comparing Fig. 2 with Fig. 3, it is clear that the casting according to this invention, that is casting under a pressure of 5 atmospheres in excess of atmospheric pressure, produced a casting much denser than the casting shown in Fig. 3. v

Aluminum alloys with from 0.5 to 15% silicon are beneficially treated by this method, it being noted that the best results are obtained with the eutectic alloys containing from 8% to 15% silicon.

The strength of the bars cast under pressure is increased as well as the density. Tests have shown that under otherwise strength of bars cast under pressure is increased from 6.5 kg./mm.= to 9.5 lkgJmm. over bars cast according to conventional methods. The test bars were machined from sandcastings having a thickness of 40 mm.

The results of fatigue tests are shown more clearly in Fig. 4. In this figure. the Wiihler curves are plotted from bar's cast from a single melt. The alloy consisted of casting. Bars 40 mm. thick were cast in sand. Curve A represents the fatigue strength of the bars cast under a pressure of 5 atmospheres in excess of atmospheric pressure according to the novel process of this invention, and curve B repequal conditions, the

:sents the same test of fatigue strength for the 11's cast at atmospheric pressure by old methods. omparison oi the curves shows that for all loads ad for all periods of load application, the test leces cast under pressure according to the presit invention are superior.

It has therefore been shown that by the instant ivention, delicate castings can be obtained, par- ,cularly from light metals, which can be used 1 places requiring lightness as well as duraility, resistance to fatigue, and strength. As hese castings can be machined without exposing orous surfaces, a great savings is obtained over astings produced by other known methods.

Therefore, it is evident that great advantages .re obtained by placing both the crucible and the nold under the same pressure before pouring, nasmuch as no additional skill is required in :ouring the melt into the mold, and no time lag :xists between the pouring and the application at pressure. The method is simple, and of prac- ;ical use in a foundry.

Having now described a means by which the Jbjects oi this invention may be obtained, what claim as new and desire to secure by Letters Patent is:

1. A process of casting metals under pressure irom a crucible to a mold which comprises passing molten metal from the crucible to the mold while simultaneously subjecting the metal in the crucible and in the mold to a pressure of at least five atmospheres in excess of atmospheric pressure.

2. A process of casting light metal alloys to form castings substantially free from pores and oi great fatigue strength comprising pouring molten metal into a mold while simultaneously subjecting both the metal being poured and the mold to substantially the same increase in atmostaining the alloy in molten form,

pheric pressure amounting to at least 5 atmospheres. p

3. A process of casting metals which com prises placing a crucible containing molten metal, and a mold for receiving the molten metal, within a pressure chamber, creating a pressure of at least five atmospheres in excess of atmospheric pressure within said chamber, and pouring the metal from the crucible into the mold while maintaining said pressure.

4. A process of casting aluminum alloyed with from 0.5% to 15% silicon which comprises placing a crucible containing the alloy in molten form, and a mold for receiving said molten alloy, within a pressure chamber, creating a pressure of at least five atmospheres in excess of atmospheric pressure within said chamber, and pouring the molten alloy from the crucible into the mold while maintaining said pressure.

5. A process of casting aluminum alloyed with from 8% to 15% silicon and further treated with sodium which comprises placing a crucible con and a mold for receiving said molten alloy, within a pressure chamber, creating a pressure of at least five atmospheres in excess of atmospheric pressure within said chamber, and pouring the molten alloy from the crucible into the mold while'maintaming said pressure.

6. A process of casting aluminum alloyed with from 0.5% to 15% silicon, manganese, magnesium and alkali metals which comprises placing a crucible containing the alloy in molten form, within a pressure chamber, creating a pressure of at least five atmospheres in excess of atmospheric pressure within said chamber, and pouring the molten alloy from the crucible into the mold while maintaining said pressure.

JOSEF DORNAUF. 

